The present invention relates in general to a fan shaft structure, and more particular, to a fan shaft structure suitable for a ceramic fan shaft, which is provided for combining firmly the fan shaft with the fan blade and preventing the combination from separation caused by long-term utilization.
Referring to FIG. 1, a perspective view of a conventional fan rotor in accordance with the prior art is shown. The fan shaft 1a has a longitudinal rod shape, with one upper end portion 10a and one lower end portion 11a. The lower end portion 11a is a free end portion. The other end portion 10a is assembled into the center part 20a of the fan blade 2a. The end portion 10a includes an annular groove portion 100a, and an end head 101a adjacent to the groove portion 100a. There are knurls 102a by roller forming on the root surface of the annular groove portion 100a. When utilizing this shaft structure to fabricate the fan rotor by insert molding, because the fan blade 2a is made of moldable plastic, the plastic resin is injected or squeezed into the annular groove portion 100a, and combines onto the knurl 102a. The center part 20a of the fan blade 2a enwraps the end portion 10a of the fan shaft 1a. The fan shaft 1a therefore combines with the fan blade 2a. Corresponding rotation between these two components is thus being eliminated.
However, this shaft structure, attaining engagement by means of the annular groove portion 100a and the knurl 102a, is suitable only for fan shaft made of metal material. It is pretty difficult to apply this art in manufacturing the ceramic fan shaft. Moreover, because the twill of the knurl 102a is shallow, the combination is not firm enough and therefore quite probable to separate. Consequently, the useful lifetime of the fan using this prior art is comparatively shorter.